The K562 leukemic cell line can be used as a model system to increase our understanding of events associated with developmental expression and regulation in normal marrow progenitor cells. Since K562 cells express embryonic and fetal hemoglobin but no adult hemoglobin, one can begin to ask questions on a molecular basis of what constitutes a transcriptionally active versus a repressed gene. Currently, I am attempting to establish an in vitro transcription system in which the transcription pattern of the globin genes mimick that observed in vivo. As an initial approach, in vitro transcriptional analysis using K562 extract, of the cloned K562 Beta-globin gene and the Gamma-globin gene was carried out. Using the K562 extract, we have demonstrated that cloned globin genes (Beta and Gamma) are transcribed in vitro indicating a lack of differential (or selective) transcription. Entertaining the possibility that differential transcription of genes may require some type of DNA conformation, K562 chromatin was used as a DNA template. While the results are preliminary, we find that proper transcriptional control similar to that observed in vivo can be demonstrated in vitro when K562 chromatin is used as a template. By S1 nuclease mapping, we demonstrated in vitro transcription of the fetal (Gamma) but no adult (Beta) globin genes. We are currently trying to increase the efficiency of chromatin transcription. The establishment of an in vitro transcription system which mimicks the K562 transcription pattern in vivo will enable us to examine molecules which surround a gene and its control region when that gene is in an active state and when it or other genes are in a repressed state.